Sometimes just clicks when try to start

OK not saying this is it but just went through this. My 87 w150 318 would do that on occasion, battery/cables were fine, cleaned terminals and flud filmed them, a few months go buy does it on occasion, Ok I am at HD picking up a BBQ and the dam starter would not disengage with the key off! OK pull the battery terminal to get it to stop. Wait a bit hit the starter a few times, put the cable back on it cranks like normal now. Get a jump, limp it home (25 miles) of white knuckles) and ok let me get into it. Fine Get a mini starter for it, wow what a difference, life is good. Well around a week later it does it again click, click crank. Ok new starter relay now not much else there right? Life is good still to this day. Well want to find out what it was I hate throwing parts at things. The solenoid plunger on the starter itself the plate is pitted and was sticking/welded and would not disengage, ok that explains why it was cranking with the key off, Then why again? Open the old starter relay up and the solenoid contacts are pitted. So it was a combination of problems. Take your time and walk away when you start getting tunnel vision and don't over think the issue. Hope it helps.